1. Field of the Invention
the present invention relates to an electronic air-fuel mixture control system for internal combustion engines, and more particularly to an electronic air-fuel mixture control system for determining an optimum air-fuel ratio in dependence upon learning values renewed in response to change of the load acting on the engine.
2. Discussion of the Background
Such an electronic air-fuel mixture control system as described above has been proposed in Japanese Patent Early Publication No. 58-150057, wherein a plurality of learning values related to a plurality of load regions are selectively renewed in response to change of the load acting on the engine so as to determine an optimum air-fuel ratio in dependence upon the renewed learning value. In such selective learning of the learning values, it is, however, observed that when the intake manifold pressure is transiently fluctuated by sudden change of the driving condition, the atmospheric pressure and the like, each of the learning values is inevitably renewed in response to such fluctuation of the intake manifold pressure. This results in transient disorder of the air-fuel ratio of the mixture.